This invention relates generally to steering wheel assemblies having airbags and, more particularly, to a tear seam in an airbag of a steering wheel assembly.
Airbags typically are located beneath a cover of a steering wheel assembly. Historically, the steering wheel was attached to the vehicle and the airbag module, which included a cover attached over the airbag, was attached.
More recently, steering wheel assemblies have been proposed wherein the steering wheel and airbag are attached to the vehicle as a modular unit. The steering wheel and airbag being assembled together prior to being shipped to the plant building the vehicle or integrating the steering wheel and airbag cover into one continuous piece. A steering wheel and airbag assembly includes a cover, a steering wheel armature, and an airbag. Most covers are formed of a synthetic plastic material that is molded over or positioned over a portion of the steering wheel armature and the airbag. The airbag is generally installed after the cover has been molded and may be installed by a manufacturer other than the manufacturer of the steering wheel armature. Thus, it is generally required that the molding process for the cover provide a cavity between the cover and a portion of the steering wheel armature to accommodate installation of the airbag.
For the airbag to deploy properly it is necessary to provide a means for the airbag to break through the cover. Typically the means provided have included tear seams located in the cover. In past designs these tear seams have generally been either H-shaped, I-shaped, or U-shaped as viewed from the driver's seat. These tear seam shapes have several disadvantages. First, the branched shapes of the tear seams require more energy and time to tear, thus the airbag must be deployed with a very high force for it to deploy and inflate rapidly enough to serve as a crash restraint. Second, these designs limit the area of opening in the cover and tend to cause the airbag to deploy straight outward rather than outward and to the sides. By allowing the airbag to expand quickly to the sides, the airbag inflates with less force and more efficiency.
Thus, it is desirable to provide a tear seam that ruptures more rapidly and that should deploy in response to a lower inflation force. It is also desirable to provide a tear seam having a reduced number of flaps of cover material when it deploys and that deploys to the sides in addition to straight outward.